Technological development has enabled tape measures of much easier use to be offered to users.
This is attained by automatic winding of the tape by an electric motor. This rapid uniform winding is of appreciable aid in all applications, and more particularly in the case of long-length tapes used by professionals concerned with measurement, such as land surveyors, quantity surveyors, inspectors and geometricians.
Such measuring instruments are already known in which the electric motor drives the spool or spindle through a high ratio mechanical reducer.
The reducer conceived in this manner has to have a high reduction ratio in order to enable small motors to be used which by their structure rotate at high speeds. In addition, for commercial reasons these reducers are required to be simple, light and cheap.
Fundamental difficulties arise, and for a long time it has been believed that the characteristics required of the high ratio reducer make its application difficult and complicated, and for this reason there has been hesitation in providing linear measuring instruments with such devices.
A further difficulty is inherent to the winding itself. At a constant angular driving speed, the linear speed of the tape varies with the beginning and end of winding, so that even in the case of average spools there are large variations in speed, for example of the order of double.
The linear speeds at the end of winding can thus attain values which require shock absorbing at the end of the tape in order to prevent damage thereto and possibly to the end ring.